JPH11102704A - Positive active material for nonaqueous electrolyte secondary battery and its evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive active material capable of obtaining a nonaqueous electrolyte battery with less deterioration in performance, even at high temperature storage. SOLUTION: This hexagonal system lithium cobalt composite oxide, a having layer structure has an ODP value of 1.065 or more but 1.080 or less when a strain of oxygen octahedron centering a cobalt atom, ODP=do-o, intra/do-o, inter, (where do-o, intra is a distance between oxygen atoms a plane formed by (a) axis and (b) axis, and do-o, inter is a distance between oxygen atoms on the outside of a plane on both sides of a cobalt atom layer) is found from an atom position coordinate obtained from Rietelt analysis result of X-ray diffraction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery using lithium, a lithium alloy or carbon as a negative electrode. The present invention relates to an active material of a nonaqueous electrolyte secondary battery having improved characteristics. The present invention also relates to a method for evaluating the positive electrode active material.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as portable telephones and notebook personal computers, there is a strong demand for the development of small, lightweight, high capacity secondary batteries having a high energy density. As such a device, there is a lithium ion secondary battery using lithium, a lithium alloy or carbon as a negative electrode, and research and development have been actively conducted.
Lithium cobalt complex oxide (LiC
Since a lithium ion secondary battery using oO ₂ ) as a positive electrode active material can obtain a high voltage of 4V class, it is expected as a battery having a high energy density, and its practical use is progressing.

[0003] In a battery using a lithium-cobalt composite oxide, many developments for obtaining excellent cycle characteristics and excellent electronic conductivity have been performed so far, and various results have already been obtained. However, when considering actual use, the power consumption of the portable device tends to increase as the capacity of the battery increases, and the battery is exposed to a high temperature state. However, little research has been made on high-temperature storage and performance, which are important battery performances in practical use, and no disclosure of inventions such as improvements relating thereto has been made.

[0004]

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a positive electrode active material capable of obtaining an excellent non-aqueous electrolyte battery with little deterioration in performance even when stored at a high temperature. It is in. A second object is to provide an evaluation method that can quickly and accurately determine the suitability of a positive electrode active material.

[0005]

Means for Solving the Problems To solve the above problems, the present inventors have studied the crystal structure and high-temperature storage of a positive electrode active material for a secondary battery comprising a lithium-cobalt double oxide determined by powder X-ray diffraction. Attention was paid to the relationship of performance at the time.

That is, the active material comprising the lithium-cobalt double oxide of the present invention is a hexagonal lithium-cobalt double oxide having a layered structure, and the atomic position obtained from the Rietveld analysis result of the X-ray diffraction. Distortion of oxygen octahedron centering on cobalt atom from coordinates (ODP = Octahedral Dis
toration Parameter) ODP = do-o, intra / do-o, inter where do-o, intra is the distance between oxygen atoms in the plane formed by the a-axis and b-axis, and do-o, inter is the Co atomic layer The distance between the oxygen atoms outside the interposed plane is determined, and the ODP value is 1.065 or more.
It is a positive electrode active material for a non-aqueous electrolyte secondary battery characterized by being 080 or less.

In the present invention, the lithium-cobalt double oxide is not limited to LiCoO ₂ , but also includes those in which part of cobalt is replaced by another atom such as boron or magnesium. When LiCoO ₂ , the ODP value is 1.07
It is set to 2 or more and 1.075 or less. When it is a B-containing lithium-cobalt double oxide, it has a composition satisfying 0 <y ≦ 0.08 in the formula LiCo _1-y B _y O ₂ and has an ODP value of 1.0.
It is 65 or more and 1.080 or less. When the Mg-containing lithium-cobalt double oxide is of the formula LiCo _1-z Mg _z O ₂
Has a composition satisfying 0 <z ≦ 0.1, and has an ODP value of 1.070 or more and 1.080 or less. In the case of a lithium cobalt complex oxide containing B · Mg, the formula Li _x Co
In _{2-xyz B y Mg z O} 2 x = 0.97~1.005, y = 0.01~
It has a composition of 0.04, z = 0.01 to 0.05, and an ODP value of 1.070 or more and 1.078 or less.

Further, the distance between the oxygen atoms outside the plane (do-o, i
nter) is 2.618 to 2.62 for LiCoO ₂
5 Å, 2.600 to 2.640 Å for B-containing lithium-cobalt double oxide, M
2.605-g for lithium-cobalt double oxide containing g
In the case of 2.630 angstroms and a lithium cobalt complex oxide containing B.Mg, the ratio is preferably 2.610 to 2.630.

Further, the present invention relates to a hexagonal lithium double oxide having the above-mentioned layered structure, wherein a plane formed by the a-axis and the b-axis from the atomic position coordinates obtained from the Rietveld analysis result of X-ray diffraction. Distance between oxygen atoms (do-o, intr
a) and the out-of-plane oxygen atom distance (do-o, inter) sandwiching the layer of cobalt Co atoms is determined, and the distortion (ODP) of the oxygen octahedron centered on the cobalt Co atoms (ODP) results in the lithium double oxide system This is a method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by judging the suitability of the active material.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various studies, the present inventors have found that there is a deep relationship between the crystal structure determined by powder X-ray diffraction and deterioration during high-temperature storage. FIG. 1A schematically shows the crystal structure of the present active material.
In particular, CoO ₂ formed from CoO ₆ octahedra sharing a ridge
The layers are called slabs (A. Rougier, C. Delmas and AV
Chadwick, Solid State Commun., 94 [2] (1995) 123-12
7.) However, the Li ions sandwiched by the slab reversibly enter and exit, whereby the charge / discharge reaction of the battery progresses and acts as an active material. Therefore, the CoO ₂ slab structure was considered to be a great guide to know the stability of the active material during the battery reaction.

Therefore, as a result of conducting various studies to achieve the above object, the present inventors have found that the structure of the oxygen octahedron shown in FIG. It has been found that there is a deep relationship with capacity deterioration. In the figure, the octahedron is written, but in fact, the length differs between the (in-plane) distance between oxygen 1 and oxygen 2 and the (inter-plane) distance between oxygen 1 and oxygen 3; The facepiece is distorted. When this distortion takes a certain value, it is presumed that the change in the crystal structure between charging and discharging is small, and lithium ions easily enter and exit, so that it is possible to suppress deterioration of the active material during high-temperature aging. did.

That is, according to the present invention, in a hexagonal lithium cobalt complex oxide having a layered structure, the distortion of an oxygen octahedron centered on a cobalt atom is determined from atomic position coordinates obtained from Rietveld analysis results of X-ray diffraction. (ODP = Octahe
dral Distoration Parameter) ODP = do-o, intra / do-o, inter where do-o, intra is the distance between oxygen atoms in the plane formed by the a-axis and b-axis, and do-o, inter is Co When the distance between out-of-plane oxygen atoms across the atomic layer is determined, the ODP value is 1.
A positive electrode active material for a non-aqueous electrolyte secondary battery, which is not less than 072 and not more than 1.075. Also, do-o, in
ter is 2.618 to 2.625 angstroms, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery is provided.

For producing the positive electrode active material of the present invention, for example, there is the following method. Stoichiometric ratio (lithium / cobalt ratio
1.0) and so as to take balance of lithium carbonate (Li ₂ CO ₃₎ and cobalt oxide (Co ₃ 0 _4), performing granulation was added and preliminarily mixed, the further PVA aqueous solution with a mixed granulator . Next, after collecting and drying the granulated material, it can be synthesized by heating it to 800 to 1000 ° C. in an air stream containing oxygen and keeping it for 10 to 20 hours. If the firing temperature is lower than 800 ° C., the reactivity of the raw material lithium carbonate is inferior, so that firing takes a long time and is uneconomical. When the firing temperature is 100
When the temperature exceeds 0 ° C., the volatilization of lithium becomes so severe that an active material having excellent stoichiometry cannot be obtained.

When part of cobalt in the lithium-cobalt double oxide is replaced with boron B, lithium carbonate and lithium carbonate are mixed so that a stoichiometric ratio (lithium / (cobalt + boron) molar ratio = 1.0) is obtained. Cobalt oxide and orthoboric acid (H ₃ BO ₃ ) may be weighed. The addition of boron promotes the grain growth of the lithium-cobalt double oxide, and improves powder handling properties and battery safety. However, since the addition of boron lowers the conductivity, it is preferable to add carbon, which is a conductive material, to a large amount.

When a part of cobalt of the lithium-cobalt double oxide is replaced with magnesium Mg, the stoichiometric ratio (lithium / (cobalt + magnesium) molar ratio = 1.0)
Lithium carbonate, cobalt oxide and basic magnesium carbonate may be weighed so that The addition of magnesium improves the conductivity of the lithium-cobalt double oxide,
This is performed to improve the utilization rate of the active material. As a compound for addition, basic magnesium carbonate, magnesium nitrate, and magnesium oxalate can be used.

In the active material of the present invention, the strain of oxygen octahedron in the CoO ₂ slab structure (O 2
DP) is in the range of 1.072 to 1.075, and do-o, inter is 2.61.
8 to 2.625 angstroms. Although the cause of the lithium-cobalt double oxide has not been identified, it is possible to suppress a change in the crystal structure at the time of charging to a low level, and to suppress deterioration (decomposition) of the active material during high-temperature storage. Conceivable. This makes it possible to obtain good aging characteristics with little deterioration in capacity even when stored at a high temperature.

[0017]

【Example】

- such that the stoichiometric ratio Synthesis of positive electrode active material sample Example 1- (lithium / cobalt ratio = 1.0), lithium carbonate were pre-crushed (Li ₂ CO _3: 99%) 3.788 kg and cobalt oxide (C
o ₃ 0 _4: Co content = 73.3%) 8.261kg mixing granulator (manufactured by Fukae Kogyo Co., and preliminarily mixed for 5 minutes using a high-speed mixer), further 963cc a 4% PVA aqueous solution Add granulation for 15 minutes. Next, the granules are collected,
After drying for an hour, this was synthesized by heating to 900 ° C. at a heating rate of 300 ° C./h in an atmosphere with an oxygen flow rate of 3.0 liter / min using a magnesia setter and holding for 15 hours.

[X-ray Diffraction] An X-ray diffraction pattern was measured using an X-ray diffractometer (RADrVB) manufactured by Rigaku Corporation. The measurement conditions were CuKα radiation (tube voltage 40 kV, tube current 150 mA).
Sampling width 0.02 °, scanning speed 4.00 ° / min
, The slits diverge 1.00 ° and scatter 1.00 ° respectively.
3 mm.

The X-ray diffraction pattern was analyzed based on the R3m crystal model using a Rietveld analysis program XReitan. Table 1 shows the obtained atomic coordinate positions and the occupancy rate of the 3a-site Li ion sites.

[0020]

[Table 1]

The distortion of the octahedron was determined by the following equation.

(Equation 1)

Here, Z indicates the oxygen atom Z-axis coordinate obtained by Rietveld analysis, and the deviation from 0.25 is the displacement amount of the oxygen atom. In Table 1, the X and Y columns also show the positions of the X and Y coordinates. a and c are lattice constants of the a-axis and the c-axis, respectively. Table 2 summarizes the lattice constants and ODP.

[Battery test] 5% by weight of acetylene black and 8% by weight of PVDF (polyvinylidene fluoride) were mixed with 87% by weight of the active material powder, and the mixture was pasted using NMP as a solvent to form a 15 mm wide Al mesh (120 mesh). The coating was performed using a blade so that the weight of the active material after drying was about 0.07 g / cm ² . This was cut into a 15 mm square to form a working electrode. Next, after vacuum drying the electrode at 120 ° C. for 12 hours, a closed test cell (1M-LiClO ₄ / (EC in electrolyte) shown in FIG. 1 provided in a glove box in an argon atmosphere (dew point −60 ° C. or less) was provided.
+ DEC), and incorporates lithium metal for the counter and reference electrodes) to obtain 4.3V vs. Charges up to Li + / Li at a current density of 1 mA / cm ² , 3.0 V vs. A capacity confirmation test was performed to discharge at a current density of 1 mA / cm ² up to Li + / Li. Then 1m
A / cm ² , 4.3Vvs. The battery was charged to Li + / Li and stored at 60 ° C. for 3 days in a sealed cell.

Thereafter, the capacity measurement of the residual discharge, charge and recovery discharge was performed under the same conditions as in the above capacity confirmation test. The deterioration rate was determined from the discharge capacity at the time of confirming the initial capacity and the discharge capacity at the time of recovery discharge. Table 2 shows the results. Deterioration rate (%) = {(initial capacity−capacity after recovery) / initial capacity} × 100

Example 2 A mixed granulated powder of lithium carbonate and cobalt oxide obtained in the same manner as in Example 1 was synthesized by firing at 950 ° C. for 15 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1.

Example 3 A mixed granulated powder of lithium carbonate and cobalt oxide obtained in the same manner as in Example 1 was synthesized by firing at 975 ° C. for 10 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1.

Comparative Example 1 A mixed granulated powder of lithium carbonate and cobalt oxide obtained in the same manner as in Example 1 was synthesized by firing in an oxygen stream at 1020 ° C. for 15 hours. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1.

Comparative Example 2 Lithium carbonate (Li ₂ CO ₃ : purity) containing coarse particles of about 10 μm so as to have a stoichiometric ratio (lithium / cobalt ratio: 1.0)
99%) 3.788kg and cobalt oxide (Co ₃ 0 _4: Co content = 73.
3%) 8.261 kg is premixed for 1 minute using a mixing granulator, and 963 cc of a 4% PVA aqueous solution is added, and granulation is performed for 15 minutes. Next, after collecting the granulated material, it was dried at 100 ° C. for 2 hours, and then heated to 950 ° C. at a heating rate of 300 ° C./h in an atmosphere of an oxygen flow rate of 3.0 liter / min using a magnesia setter. It was synthesized by holding for 15 hours.

Comparative Example 3 A mixed granulated powder of lithium carbonate and cobalt oxide obtained in the same manner as in Example 1 was synthesized by firing at 850 ° C. for 20 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1.

[0030]

[Table 2]

As can be seen from Table 2, the lithium-cobalt double oxide according to the present invention whose ODP value falls within a predetermined range is as follows:
It can be seen that when used as an active material of a lithium secondary battery, a battery having a high capacity retention ratio during high-temperature storage can be obtained. On the other hand, the lithium-cobalt double oxide of the comparative example in which the ODP value does not fall within the range of the present invention even when synthesized from the same raw material had a poor capacity retention ratio when used as an active material.

Example 4 From this example to Comparative Example 5, boron-containing lithium-cobalt double oxide is used as a positive electrode active material. [Synthesis of Positive Electrode Active Material Sample] 3.8 kg of the lithium carbonate and 7.95 kg of cobalt oxide which had been pre-ground so as to have a stoichiometric ratio (lithium / (cobalt + boron) ratio = 1.0). , orthoboric acid (H ₃ BO ₃₎ 0.19k
g. These are weighed so that y = 0.03 in terms of the formula LiCo ₁ -yB _y O ₂ .
The weighed materials are blended, premixed for 5 minutes using a mixing granulator, and 950 cc of a 4% PVA solution is added, followed by granulation for 15 minutes. Next, the granules are collected and dried by heating.
It was synthesized by holding at 15 ° C. for 15 hours.

[X-ray Diffraction] As in Example 1, the X-ray diffraction pattern was measured, and the X-ray diffraction pattern was subjected to Rietveld analysis. Table 3 shows the obtained atomic coordinate positions and the 3a-site Li ion occupancy.

[0034]

[Table 3]

Table 4 summarizes the lattice constant and ODP. [Battery test] 5% by weight of acetylene black and 8% by weight of PVDF were mixed with 87% by weight of these active material powders, and a capacity confirmation test was performed in the same manner as in Example 1 to measure the remaining discharge, charge and recovery discharge capacity. The test was performed under the same conditions as the capacity confirmation test. The capacity deterioration rate was determined from the discharge capacity at the time of confirming the initial capacity and the discharge capacity at the time of the recovery discharge. Table 4 shows the results.

Example 5 3.8 kg of lithium carbonate, 8.159 kg of cobalt oxide and 0.032 kg of orthoboric acid were mixed. These are of the formula LiCo _{1- y By}
It is weighed so that y = 0.005 in terms of O ₂ . The formulation was mixed in the same manner as in Example 4, and synthesized by firing at 900 ° C. for 15 hours in an oxygen stream.
XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 4 shows the results.

Example 6 3.8 kg of lithium carbonate, 7.79 kg of cobalt oxide and 0.315 kg of orthoboric acid were blended. These are of the formula LiCo _{1- y By}
It is weighed so that y = 0.05 in terms of O ₂ . The composition was mixed in the same manner as in Example 4 and synthesized by firing at 950 ° C. for 10 hours in an oxygen stream.
XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 4 shows the results.

Comparative Example 4 The mixed granulated powder obtained in the same manner as in Example 4 was synthesized by firing at 900 ° C. for 8 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 4 shows the results.

Comparative Example 5 Lithium carbonate (Li ₂ CO ₃ : 99% purity) 3.8 kg, cobalt oxide (Co ₃ O ₄ : Co content 73.3%) 8.11
8 kg, orthoboric acid (H ₃ BO ₃ : purity 99.5%)
063 kg was compounded. These were weighed so that y = 0.01 in terms of the formula LiCo _{1 over y} B y O _2. The formulation is mixed as in Example 4 and
The synthesis was performed by heating to 00 ° C. and holding for 20 hours. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 4 shows the results.

[0040]

[Table 4]

As described above, when the B-containing lithium-cobalt double oxide according to the present invention is used as an active material of a lithium secondary battery, a battery having a high capacity retention rate during high-temperature storage can be obtained. .

Example 7 Examples 7 to 6 are examples in which a magnesium-containing lithium-cobalt double oxide is used as a positive electrode active material. [Synthesis of positive electrode active material sample] 3.8 kg of lithium carbonate preliminarily pulverized and 7.954 kg of cobalt oxide so as to have a stoichiometric ratio (lithium / (cobalt + magnesium) molar ratio = 1.0), Basic magnesium carbonate (M
g content: 25.2 wt%) 0.295 kg was weighed.
These are calculated as z = 0.0 in terms of the formula LiCo _1-z Mg _z O _2.
It was weighed to be 3. The weighed materials are blended, premixed for 5 minutes using a mixing granulator, and 960 cc of a 4% PVA solution is added, followed by granulation for 15 minutes.
Next, the granulated product is collected, dried at 100 ° C. for 2 hours, and then heated at a heating rate of 300 ° C./min using a magnesia setter.
It was synthesized by heating to 00 ° C. and holding for 15 hours.

[X-ray Diffraction] As in Example 1, the X-ray diffraction pattern was measured, and the X-ray diffraction pattern was subjected to Rietveld analysis. Table 5 shows the obtained atomic coordinate positions and the 3a-site Li ion occupancy.

[0044]

[Table 5]

Table 6 summarizes the lattice constants and ODP. [Battery test] 5% by weight of acetylene black and 8% by weight of PVDF were mixed with 87% by weight of these active material powders, and a capacity confirmation test was performed in the same manner as in Example 1 to measure the remaining discharge, charge and recovery discharge capacity. The test was performed under the same conditions as the capacity confirmation test. The deterioration rate was determined from the discharge capacity at the time of confirming the initial capacity and the discharge capacity at the time of recovery discharge. Table 6 shows the results.

Example 8 3.8 kg of lithium carbonate, 8.036 kg of cobalt oxide and 0.197 kg of basic magnesium carbonate were mixed. These are of the formula LiCo
_It is weighed so that z = 0.02 in terms of _1-z Mg _z O ₂ . The formulation was mixed as in Example 7,
The obtained mixed granulated powder was synthesized by firing at 900 ° C. for 15 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 6 shows the results.

Example 9 3.8 kg of lithium carbonate, 7.79 kg of cobalt oxide and 0.492 kg of basic magnesium carbonate were blended. These are of the formula Li
It is weighed so that z = 0.05 in terms of Co _1-z Mg _z O ₂ . The mixture was mixed in the same manner as in Example 7, and the obtained mixed granulated powder was heated at 950 ° C and 1 ° C in an oxygen stream.
It was synthesized by firing for 0 hours. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in Example 1.
The same was done. Table 6 shows the results.

Comparative Example 6 3.8 kg of lithium carbonate, 7.38 kg of cobalt oxide and 0.983 kg of basic magnesium carbonate were blended. These are of the formula Li
It is weighed so that z = 0.102 in terms of Co _1-z Mg _z O ₂ . The mixture was mixed in the same manner as in Example 7, and the obtained mixed granulated powder was heated at 950 ° C and 1 ° C in an oxygen stream.
It was synthesized by firing for 0 hours. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in Example 1.
The same was done. Table 6 shows the results. As described above, it is understood that when the Mg-containing lithium-cobalt double oxide according to the present invention is used as an active material of a lithium secondary battery, a battery having a high capacity retention rate during high-temperature storage can be obtained.

[0049]

[Table 6]

Example 10 Examples 10 to Comparative Example 8 are examples in which a lithium-cobalt double oxide containing boron and magnesium is used as a positive electrode active material. [Synthesis of lithium carbonate, cobalt oxide, the total orthoboric acid and basic magnesium carbonate and 12 kg, formula _{Li x Co 2-xyz B y} Mg z in _{O 2 x = 1.0, y =} 0.0
2, weighed so that z = 0.04, then premixed using a mixing granulator in the same manner as in Example 1, granulated, collected granules, dried by heating, and then heated to 900 ° C. For 15 hours.

[X-ray Diffraction] As in Example 1, the X-ray diffraction pattern was measured, and the X-ray diffraction pattern was subjected to Rietveld analysis. Table 7 shows the obtained atomic coordinate positions and the 3a-site Li ion occupancy.

[0052]

[Table 7]

Table 8 summarizes the lattice constants and ODP. [Battery test] 5% by weight of acetylene black and 8% by weight of PVDF were mixed with 87% by weight of these active material powders, and a capacity confirmation test was performed in the same manner as in Example 1 to measure the remaining discharge, charge and recovery discharge capacity. The test was performed under the same conditions as the capacity confirmation test. The deterioration rate was determined from the discharge capacity at the time of confirming the initial capacity and the discharge capacity at the time of recovery discharge. Table 8 shows the results.

Example 11 A mixed granulated powder obtained in the same manner as in Example 10 was synthesized by firing at 950 ° C. for 15 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 8 shows the results.

[0055] - Example 12 Lithium carbonate, cobalt oxide, orthoboric acid, and a basic magnesium carbonate formula _{Li x Co 2-xyz B y} Mg z O
_In Example 2, the mixture was weighed so that x = 0.98, y = 0.01, and z = 0.04, and the mixed granulated powder obtained in the same manner as in Example 10 was calcined at 950 ° C. for 10 hours in an oxygen stream. Synthesized. XR of the obtained lithium cobalt complex oxide
D evaluation and battery evaluation were performed in the same manner as in Example 1. Table 8 shows the results.

Comparative Example 7 A mixed granulated powder of lithium carbonate and cobalt oxide obtained in the same manner as in Example 10 was synthesized by firing at 1050 ° C. for 15 hours in an oxygen stream. XRD evaluation and battery evaluation of the obtained lithium-cobalt double oxide were performed in the same manner as in Example 1. Table 8 shows the results.

[0057] - Comparative Example 8 Lithium carbonate, cobalt oxide, orthoboric acid, and basic magnesium carbonate of formula _{Li x Co 2-xyz B y} Mg z O
_{In 2} , weigh each so that x = 0.96, y = 0.05, z = 0.03, and use 750 g of YSZ (yttria-stabilized zirconia) balls having a diameter of 10 mm, using a 400 cc ball mill container, and further adding 100 cc of distilled water. The grinding and mixing were performed at a rotation speed of 85 rpm for 15 hours. The YSZ ball and the slurry are separated using a sieve, pre-dried at 80 ° C. for 2 hours, and then dried at 100 ° C. for 1 hour. This was heated using a magnesia setter at an oxygen flow rate of 0.3 l / min and a heating rate of 300 ° C / min.
The synthesis was carried out by heating to 900 ° C. for 20 hours and holding for 20 hours. XRD of the obtained lithium cobalt complex oxide
Evaluation and battery evaluation were performed in the same manner as in Example 1. Table 8 shows the results.

[0058]

[Table 8]

As described above, it can be seen that when the lithium-cobalt double oxide according to the present invention is used as an active material of a lithium secondary battery, a battery having a high capacity retention rate during high-temperature storage can be obtained.

Note that the batteries in each of the above embodiments are Li
Although it was a battery using a metal as a negative electrode, the use of the active material of the present invention is not limited to this. For the negative electrode, carbon fiber, graphite, etc., capable of reversibly intercalating Li by a battery reaction are used. Can also be used.

[0061]

By using the lithium-cobalt double oxide according to the present invention as a positive electrode active material of a non-aqueous secondary battery, a secondary battery having an excellent capacity retention rate at high temperature storage can be manufactured.

[Brief description of the drawings]

FIG. 1 schematically shows the crystal structure of a lithium-cobalt double oxide, (a) is an overall view thereof, and (b) is a C-form thereof.
FIG. 3 is an enlarged view of an oxygen octahedron in an oO ₂ slab.

FIG. 2 is a longitudinal sectional view of a beaker type battery used for a charge / discharge capacity test.

[Explanation of symbols]

 1. Beaker 2. Electrolyte 3. Teflon stopper 4. Positive electrode 5. Counter electrode (Li metal) 6. Reference electrode (Li metal)

Claims (10)

[Claims] 1. In a hexagonal lithium-cobalt double oxide having a layered structure, distortion of an oxygen octahedron centered on a cobalt atom is determined from atomic position coordinates obtained from Rietveld analysis results of X-ray diffraction (ODP = Octahedral Distoration P
arameter) ODP = do-o, intra / do-o, inter where do-o, intra is the distance between oxygen atoms in the plane formed by the a-axis and b-axis, and do-o, inter is the Co atomic layer When the distance between out-of-plane oxygen atoms was determined, the ODP value was 1.065 or more and 1.080 or more.
A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that: 2. The lithium-cobalt double oxide is LiCo.
A O _2, a positive electrode active material for non-aqueous electrolyte secondary battery according to claim 1 ODP value is 1.072 or more 1.075 or less. 3. An out-of-plane oxygen atom distance do− calculated from atomic coordinates and lattice constant obtained by Rietveld analysis.
3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein o, inter is 2.618 to 2.625 angstroms. 4. The method according to claim 1, wherein the lithium-cobalt double oxide has the formula LiC.
In o _{1 over y B y O 2, 0 <} B containing lithium cobalt complex oxide is y ≦ 0.08 ODP value is 1.065 to 1.0
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which is 80 or less. 5. An out-of-plane oxygen atom distance do− calculated from atomic coordinates and lattice constants obtained by Rietveld analysis.
The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 4, wherein o, inter is 2.600 to 2.640 angstroms. 6. The lithium-cobalt double oxide of the formula LiC
o _{1 -z} Mg _z O ₂ is a Mg-containing lithium-cobalt double oxide satisfying 0 <z ≦ 0.1, and having an ODP value of 1.07
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is 0 or more and 1.080 or less. 7. An out-of-plane oxygen atom distance do− calculated from atomic coordinates and lattice constants obtained by Rietveld analysis.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein o, inter is 2.605 to 2.630 angstroms. 8. The method according to claim 8, wherein said lithium-cobalt double oxide is Li _x C
In _{o 2-xyz B y Mg z} O 2, x = 0.97~1.005, y = 0.
The nonaqueous electrolyte secondary battery according to claim 1, wherein the B / Mg-containing lithium-cobalt double oxide has an ODP value of 1.070 or more and 1.078 or less, wherein 01-0.04 and z = 0.01-0.05. Positive electrode active material. 9. An out-of-plane oxygen atom distance do− calculated from atomic coordinates and lattice constants obtained by Rietveld analysis.
The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 8, wherein o, inter is 2.610 to 2.630 angstroms. 10. A hexagonal lithium double oxide having a layered structure according to claim 1, wherein an in-plane formed by an a-axis and a b-axis based on atomic position coordinates obtained from a Rietveld analysis result of X-ray diffraction. Distance between oxygen atoms (do-o, intra) and out-of-plane distance between oxygen atoms (do-o, inter) sandwiching a layer of cobalt Co atoms were calculated, and the strain of oxygen octahedra centered on cobalt Co atoms was determined. A method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: judging suitability of the lithium double oxide-based active material by (ODP).